1. Technical Field
The present invention relates to a light source device and a projector including the light source device.
2. Related Art
As disclosed in JP-A-2008-226570, a light source device which includes a sub mirror in an arc tube to use light emitted from the arc tube with high efficiency is known. This sub mirror is fixed to the arc tube by an adhesive.
According to the light source device having the sub mirror fixed to the arc tube, air for cooling a tube spherical portion (cooling air) is difficult to be supplied between the arc tube (particularly the tube spherical portion) and the sub mirror. Thus, when cooling (air supply) is provided by using a cooling fan, the temperature of the tube spherical portion is difficult to be properly controlled by the air supply. Moreover, the temperature difference between the upper area of the tube spherical portion (particularly the highest portion of the upper side) and the lower area (particularly the lowest portion of the lower side) increases.
When air is supplied to adjust the temperature of the upper area of the tube spherical portion to an appropriate temperature with the increased temperature difference between the upper area and the lower area of the tube spherical portion, the temperature of the lower area of the tube spherical portion is excessively lowered. In this case, the lower area of the tube spherical portion may be blackened. On the contrary, when air is supplied to adjust the temperature of the lower area of the tube spherical portion to an appropriate temperature, the temperature of the upper area of the tube spherical portion is excessively raised. In this case, the upper area of the tube spherical portion may be whitened. When these phenomena are produced, the areas of the tube spherical portion corresponding to the phenomena lose transparency. Thus, both blackening and whitening are considered to be factors that decrease the light amount of the arc tube.
The whitening herein refers to a phenomenon which whitens a base material constituting the tube spherical portion at the time of recrystallization caused by the high temperature. The blackening refers to a phenomenon where evaporated atoms of a base material constituting an electrode (such as tungsten atoms) do not return to the electrode but adhere to the inner wall of the tube spherical portion when a halogen cycle of the base material is not performed due to the low temperature. When the whitening or blackening develops, the area corresponding to the whitening or blackening absorbs heat and breaks the tube spherical portion in some cases.
Therefore, such a light source device and a projector have been demanded which can efficiently cool the tube spherical portion even when the sub mirror is provided, and can decrease the temperature difference between the upper area and the lower area of the tube spherical portion.